The longitudinal cross-sectional shape of an airfoil, such as an airplane wing, as defined by the disposition of the mean-camber line and the distribution of thickness along the chord line, determines in part the aerodynamic properties of the airfoil and the aircraft. The chord line of the airfoil is defined by the straight line interconnecting the leading edge of the airfoil and its trailing edge. The mean-camber line of the airfoil is the line representing the locus of points disposed equidistantly between the top and bottom surfaces of the airfoil, and in conjunction therewith, the camber of the airfoil is the distance that the mean-camber line deviates from the chord line.
It has been found that a thick or highly cambered airfoil has a larger lift coefficient than that of a less cambered or thinner airfoil. However, a highly cambered airfoil also exhibits greater resistance or drag than that of a less cambered airfoil when the aircraft is in high speed flight.
Various adjustable airfoil assemblies have been proposed heretofore for converting the aircraft from high lift performance at relatively low speed to reduced lift performance and reduced drag at higher speeds.
For example, U.S. Pat. Nos. 1,803,915 to Parmele, 1,225,711 to Holle, 3,806,065 to Custer, 1,747,637 to Larsen and 2,349,858 to Gillmor show aircraft wings with an adjustable top for changing the wing's profile and wind resistance.
U.S. Pat. No. 1,631,259 to Gilmore shows an airfoil with a pivotally adjustable front nose which is changeable between a relatively blunt leading edge and a pointed leading edge.
U.S. Pat. No. 4,007,896 to Reynolds shows an adjustable flap at the trailing edge of a fixed wing for controlling the lift and drag.
U.S. Pat. Nos. 1,845,960 to Daniell and 1,881,159 to Apolloniou show pivotally adjustable panels which normally fit in the top of an aircraft wing but can be raised for braking purposes.